The long-term goal of this project is to understand the molecular mechanisms which cause embryonic cells to adopt particular fates as a function of their position in the embryo. The process to be studied is the establishment of the dorsal-ventral pattern of the Drosophila embryo, where genetic, embryological and molecular techniques can be combined to characterize the function of individual gene products. One maternal effect gene which appears to play a central role in the establishment of embryonic dorsal-ventral polarity, Toll, will be studied in detail. Genetic studies will include isolating new recessive Toll alleles and studying the phenotypes produced by Toll alleles combined with other mutations affecting the embryonic dorsal-ventral pattern. Mutant alleles of Toll will be characterized by their phenotype and by the response of mutant embryos to the injection of wild type cytoplasm. The Toll gene will be cloned, and mutations which perturb Toll function in defined ways will be mapped onto the DNA.